I have never used a sparklan AP before, however as long as it supports acting as a repeater then you should have no problem. Your existing AP must also support repeaters, which most recent AP do.

Because your old AP only works in 802.11b, you may have issues working with your existing AP (Assuming it works in 802.11g), however you should be able to tell it to work in 802.11b/g and it should work. not 100% sure on this, will have to try it.

I have always used the same brand AP and definitely same standard (802.11g) if im setting up a AP with a repeater.